The Fulde-Ferrell-Larkin-Ovchinnikov State in Pnictides

Fe-based superconductors (FeSC) exhibit all the properties of systems that allow the formation of a superconducting phase with oscillating order parameter, called the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. By the analysis of the Cooper pair susceptibility in two-band FeSC, such systems are shown to support the existence of a FFLO phase, regardless of the exhibited order parameter symmetry. We also show the state with nonzero Cooper pair momentum, in superconducting FeSC with similar to cos(k (x) )a <...cos(k (y) symmetry, to be the ground state of the system in a certain parameter range.